Organic electroluminescence display device and producing method thereof

ABSTRACT

In manufacturing of an organic electroluminescence (EL) display device, after first electrodes are formed on a substrate, insulating films are formed on the first electrodes except regions corresponding to light emitting portions. Spacers are formed on the insulating films, and overhanging portions are formed so as to overhang the spacers. Thus, element isolating structure portions for isolating organic EL elements are formed. Then, organic EL films, second electrodes, and protecting films are sequentially formed between the spacers. In the thus formed light emitting portions of the organic EL display device, the bending angle of a bending portion of a pattern of the element isolating structure portion is larger than 90°.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an organic electroluminescencedisplay device which is used as a display device or a light source andwhich can be formed by a process including photolithography with easyisolation of organic electroluminescence elements, and also relates to aproducing method of the above organic electroluminescence displaydevice.

[0003] 2. Description of the Related Art

[0004] At present, liquid crystal display devices are used as thin flatpanel displays which are currently the main stream of the technicalfield of display devices. However, organic electroluminescence(hereinafter referred to “organic EL”) display devices using organic ELelements are superior to liquid crystal display devices in the followingpoints:

[0005] (1) Having a wide viewing angle because the organic EL elementsemit light by themselves.

[0006] (2) Allowing easy manufacture of a thin display device of about2-3 mm in thickness.

[0007] (3) Capable of providing a natural emission color because of noneed for using any polarizing plate.

[0008] (4) Capable of clear display because of a wide light and shadedynamic range.

[0009] (5) Allowing organic EL elements to operate in a wide temperaturerange.

[0010] (6) Easily enabling dynamic image display because the responsespeed of the organic EL elements is three orders or more higher thanthat of liquid crystal elements.

[0011] In spite of the above advantages, the organic EL display deviceshave the following problems in manufacture. For example, organic layersconstituting the organic EL elements and electrodes containing a metalhaving a small work function which is usually used as a cathode toinject electrons into the organic layers are easily deteriorated bywater and oxygen. Further, the organic layers are easily dissolved by asolvent and are not resistant to heat.

[0012] In a manufacturing method using water, organic solvents, andheat, it is difficult to isolate or divide elements after the formationof organic layers and an electrode containing a metal having a smallwork function. Therefore, when it is intended to form an organic ELdisplay device in the same class as liquid crystal display devicescurrently implemented, the matured semiconductor manufacturingtechnology and liquid crystal display device manufacturing technologycannot be applied as they are to isolate small organic EL elements.

[0013] In the above circumstance, a method has been proposed in whichwalls higher than films constituting organic EL films are formed betweendisplay line electrodes to be isolated, and materials for forming theorganic EL films are vacuum-evaporated in a direction not perpendicularto the substrate surface (i.e., evaporated obliquely). This methodutilizes the fact that the materials for forming the organic EL filmsare not formed in the portions shielded by the high walls. (Refer toU.S. Pat. Nos. 5,276,380 and 5,294,869.)

[0014] In the above method, it is very important that the directions inwhich atoms or molecules travel from the evaporation source to thesubstrate be aligned. As shown in FIG. 8, in an ordinary evaporationmethod, an evaporation material is vaporized to assume concentricspheres with an evaporation source 101 in which the evaporation materialis set as the center, and then attaches to a substrate 100. The incidentangle of the evaporation material with respect to the substrate 100varies with the position on the substrate 100, and the thickness of aresulting film formed on the substrate 100 varies in response to thedistance from the evaporation source 101.

[0015] Therefore, it is difficult for the above method to isolate thedisplay line electrodes in a stable manner, and to form the filmsuniformly over the entire substrate surface. Although the above methodcould manufacture small-size display devices, in order to apply theabove method to medium-size or large-size substrates of the 10-inchclass or larger, for example, the distance between the substrate 100 andthe evaporation source 101 should be set sufficiently long. In thiscase, the size of the evaporation apparatus becomes impractical.

[0016] Even if such a large evaporation apparatus is produced, a largeamount of organic EL material does not reach the substrate surface, andthus is consumed in vain without being formed on the substrate,resulting in a major factor of cost increase.

[0017] In general, a substrate is rotated or a plurality of evaporationsources are used to evaporate a thin film uniformly on the substrate.These methods are actually employed in semiconductor devicemanufacturing processes and liquid crystal device manufacturingprocesses. However, if the above method of forming high walls is appliedto these methods, the element isolation cannot be attained any more.

[0018] In the conventional method, the organic EL films and the metalelectrodes having a small work function are necessarily exposed unlessprotecting layers are consecutively formed in the same direction. Thus,it is difficult to completely eliminate the influences of water, oxygen,etc. It is impossible to perform photolithography having a process usingan organic solvent or water after formation of the organic EL films.

SUMMARY OF THE INVENTION

[0019] An object of the present invention is to provide a highlyreliable organic EL display device and a producing method thereof bymaking the element isolation easier irrespective of the manner ofevaporating an organic EL material, enabling the use of a large-sizesubstrate, and completely covering organic EL layers and metalelectrodes having a small work function by forming films that are stablewith respect to water, oxygen, and organic solvents without exposingthose to the air, i.e., in a vacuum.

[0020] According to the present invention, there is provided an organicelectroluminescence display device comprising: a first electrode whichis transparent and formed on a substrate; an insulating film selectivelyformed on the first electrode; a plurality of spacers formed on theinsulating film; an overhanging film which is formed on each spacer andhas a width wider than that of each spacer; an organicelectroluminescence film formed on the first electrode and betweenadjacent spacers; and a second electrode formed on the organicelectroluminescence film.

[0021] According to the present invention, there is provided a methodfor producing an organic electroluminescence display device, comprisingthe steps of: forming a first electrode which is transparent on asubstrate; selectively forming an insulating film on the firstelectrode; forming a spacer film on the insulating film; selectivelyforming a photosensitive film on the spacer film; forming a plurality ofspacers by overetching the spacer film, so that the photosensitive filmoverhangs each spacer; forming an organic electroluminescence film onthe first electrode and between adjacent spacers; and forming a secondelectrode on the organic electroluminescence film.

[0022] According to the present invention, there is provided an organicelectroluminescence display device comprising: a plurality of organicelectroluminescence elements; and an element isolating structure portionwhich is formed between adjacent organic electroluminescence elementsand has an overhanging portion, wherein a bending portion of the elementisolating structure portion has a bending angle larger than 90°.

[0023] According to the present invention, there is provided an organicelectroluminescence display device comprising: a plurality of organicelectroluminescence elements; and an element isolating structure portionwhich is formed between adjacent organic electroluminescence elementsand has an overhanging portion, wherein a bending portion of the elementisolating structure portion is formed by an arc having a radius ofcurvature of 5 μm.

[0024] According to the present invention, there is provided a methodfor producing an organic electroluminescence display device having anelement isolating structure portion formed between adjacent organicelectroluminescence elements, a bending portion of the element isolatingstructure portion having a bending angle larger than 90°, the methodcomprising the steps of: forming a first electrode which is transparenton a substrate; selectively forming an insulating film on the firstelectrode; forming a spacer film on the insulating film; selectivelyforming a photosensitive film on the spacer film; forming a plurality ofspacers overhung by the photosensitive film by overetching the spacerfilm, to obtain the element isolating structure portion; forming anorganic electroluminescence film on the first electrode and betweenadjacent spacers; and forming a second electrode on the organicelectroluminescence film.

[0025] According to the present invention, there is provided an organicelectroluminescence display device comprising: a first electrode whichis transparent and formed on a substrate; an insulating film selectivelyformed on the first electrode; a plurality of first spacers formed onthe insulating film; a plurality of second spacers formed on the firstspacers; an overhanging film which is formed on each second spacer andhas a width wider than that of each first spacer; an organicelectroluminescence film formed on the first electrode and betweenadjacent first spacers; and a second electrode formed on the organicelectroluminescence film.

[0026] According to the present invention, there is provided a methodfor producing an organic electroluminescence display device, comprisingthe steps of: forming a first electrode which is transparent on asubstrate; selectively forming an insulating film on the firstelectrode; forming a spacer film having a plurality of layers on theinsulating film; selectively forming a photosensitive film on the spacerfilm;forming a plurality of spacers by overetching one layer of thespacer film which is not in contact with the photosensitive film, sothat the photosensitive film overhangs each spacer; forming an organicelectroluminescence film on the first electrode and between adjacentspacers; and forming a second electrode on the organicelectroluminescence film.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIGS. 1A and 1B show the structure of an organicelectroluminescence (EL) elements according to a first embodiment of theinvention;

[0028]FIG. 2 is a diagram explaining rotary evaporation;

[0029] FIGS. 3A-3J and 4A-4C show a manufacturing process of the organicEL element according to the first embodiment of the invention;

[0030] FIGS. 5A-5E and 7A-7B show a manufacturing process of organic ELelements according to a second embodiment of the invention;

[0031]FIG. 6 is a plan view of a color filter portion of an organic ELdisplay device according to the second embodiment of the invention;

[0032]FIG. 8 is a diagram explaining an ordinary evaporation method;

[0033]FIGS. 9A and 9B are a plan pattern view and a sectional view oflight emitting portions of an organic EL display device according to athird embodiment of the invention;

[0034]FIGS. 10A and 10B are a plan pattern view and a sectional view oflight emitting portions of an organic EL display device according to afourth embodiment of the invention;

[0035] FIGS. 11A-11C are plan pattern views of a display portion of anorganic EL display device according to a fifth embodiment of theinvention;

[0036] FIGS. 12A-12H are plan pattern views and sectional views of a bargraph portion of the display portion of the organic EL display deviceaccording to the fifth embodiment of the invention;

[0037] FIGS. 13A-13C and 14A-14C are plan pattern views and sectionalviews of a light emitting portion of an organic EL display device havingelement isolating structure portions according to the invention;

[0038]FIG. 15 shows the chemical structural formula of N,N′-bis(m-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine;

[0039]FIG. 16 shows the chemical structural formula oftris(8-hydroxyquinoline) aluminium;

[0040]FIG. 17 shows the chemical structural formula ofpoly(tiophene-2,5-diyl);

[0041]FIG. 18 shows the chemical structural formula of rubrene;

[0042]FIG. 19 shows the chemical structural formula of 4,4′-bis[(1,2,2′-trisphenyl)ethenyl]-biphenyl; and

[0043]FIG. 20 shows an organic EL element according to the inventionwith a harder film which is used as a support film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] Embodiments of the present invention will be hereinafterdescribed in detail with reference to the accompanying drawings.

Embodiment 1

[0045]FIGS. 1A and 1B show the structure of organic electroluminescence(EL) elements according to a first embodiment of the invention. As shownin FIG. 1A, a first transparent electrode 2 (for example, an indium tinoxide (ITO) film) is formed on an insulating transparent substrate 1 ina desired pattern shape. Then, an insulating film (for example, apolyimide film or an SiO₂ film) is formed on the first transparentelectrode 2. Organic EL films and second electrodes contacting with theorganic EL films will be formed later to constitute a light emittingportion. A portion of the insulating film located on the display surfaceside of the light emitting portion is removed.

[0046] Next, a spacer film (for example, a polyimide film) constitutedof at least one layer is formed. After photosensitive films(photosensitive resin films) such as resists are formed betweenelectrodes to be isolated, photosensitive films 5 on remaininginsulating films 3 are left by photolithography. Subsequently, theexposed portions of the spacer film are removed by etching. At thistime, the portions of the spacer film under the photosensitive films 5are also removed to form sufficiently long undercut regions. As aresult, with respect to the spacers 4 formed by undercutting, thephotosensitive films 5 assumes eaves, hat, or cap-shaped structure, oran overhanging structure in general terms. Thus, element isolatingstructure portions can be formed.

[0047] By forming the element isolating structure portions, when organicEL films 6 which control light emission and carriers and secondelectrodes 7 directly contacting with the organic EL films 6 are formedby evaporation, as shown in FIG. 1B, the elements can always be isolatedirrespective of the positional relationship between the evaporationsource and the substrate and the method for improving the uniformity ofthe films. Thus, a method that regards, as most important, improving theuniformity of the organic EL films 6 formed, such as a rotary method inthe case of evaporation, can be selected.

[0048] After the organic EL films 6 and the second electrodes 7 directlycontacting with the organic EL films 6 are formed in the above manner,metal films 8 made of a stable metal that is hardly affected by water,oxygen, or organic solvents are formed as protecting films for thesecond electrodes 7. When the organic EL films 6 and the secondelectrodes 7 are formed by evaporation, the metal films 8 are formed bya method (for example, sputtering) that provides resulting films withbetter step coverage than evaporation.

[0049] The protecting film may be any of a metal film of a stable metalsuch as aluminum (Al), an insulating film such as an SiO₂ film, and acombination of an Al film and a second protecting film 9 such as an SiO₂film formed thereon (see FIG. 1B). The second protecting film 9 protectsthe organic EL film 6, the second electrode 7, the metal film 8, andother films.

[0050] It is desirable to form the protecting film subsequently to theformation of the organic EL film 6 and the second electrode 7 withoutbeing exposed to the air, i.e., with maintaining a vacuum state. Forexample, the protecting film may be formed by evaporation in a lowvacuum or sputtering. A film having good step coverage can be formed byrotating the substrate 1 while it is considerably inclined from thedirection of vaporization from an evaporation source 10 as shown in FIG.2.

[0051] Thus, the structure of FIG. 1B is obtained in which even the endportions of the organic EL films 6 and the second electrodes 7 are notexposed by forming the metal films 8 as the protecting films or themetal films 8 and the second protecting films formed thereon so thatthey are also formed in the above undercut regions. Since the organic ELfilms 6 are completely enclosed by the first transparent electrodes 2,the insulating films 3, and the metal films 8 (and the protecting films9), the organic EL elements can resist through a process using water oran organic solvent, such as photolithography that is performed informing lead out electrodes for the metal electrodes 8.

[0052] It is apparent from the above description that it becomespossible to cause the organic EL elements to emit light uniformly, tomanufacture a highly reliable organic EL flat panel display at a stableyield, and to increase the flexibility of the manufacturing process ofan organic EL flat panel display.

[0053] The first embodiment of the invention will be described in moredetail. FIGS. 3A-3J and 4A-4C show a manufacturing process of theorganic EL elements according to the first embodiment of the invention.This process is directed to a case of manufacturing a 2-row/16-columndot matrix type display device in which the 1-dot pixel size is 0.4mm×0.6 mm and the character display area is 5×8 dots.

[0054] An inexpensive soda glass substrate, which is used in amorphoussilicon (a-Si) solar cells, super twisted nematic (STN) liquid crystaldisplay devices, etc., is used as the substrate of the organic ELdisplay device. The entire surface of the glass substrate is coated withsilica (SiO₂). The silica coating prevents sodium elution from the glasssubstrate when it is heated, protects the soda glass substrate which isnot resistant to acids and alkalis, and improves the flatness of theglass substrate surface. For example, the silica coating is performed byimmersing the glass substrate in a SiO₂ solution or by spin on glass(SOG) coating for the glass substrate.

[0055] Next, an ITO film which is a transparent conductive film as afirst electrode is formed at a thickness of about 1,500 angstrom bysputtering on the glass substrate. The use of the ITO film is due to thefact that it exhibits superior characteristics to films made of othermaterials when it is used as a transparent conductive film. However, atransparent electrode of a ZnO film, an SnO₂ film, or the like may beused if it has transmittance and resistivity, for example, that will notcause any problem during use. When the ITO film is formed over a largearea, sputtering is advantageous in uniformity and film quality of aresulting film as well as productivity. However, the ITO film need notalways be formed by sputtering, and may be formed by evaporation, forexample.

[0056] As shown in FIGS. 3A and 3F, after the ITO film is formed on thesilica-coated substrate 1 (the silica coating film is not shown), aresist pattern (not shown) is formed on the ITO film byphotolithography. After unnecessary portions of the ITO film are removedby etching to form the ITO film into a desired electrode pattern, theresist pattern is removed. As shown in FIG. 3A in enlarged form, it isdesired that the ends of the ITO films 2 be tapered. This is to prevent,in the step portions of the ITO films 2, step disconnection of organicfilms and second electrodes to be evaporated in later processes, tothereby improve the yield and life of the organic EL elements. It isdesired that the taper angle be 45° or less. Incidentally, FIGS. 3F-3Jare plan views of element patterns, and FIGS. 3A-3E are sectional-viewstaken along dot-chain lines A-A′, B-B′, C-C′, D-D′, and E-E′ in FIGS.3F-3J, respectively.

[0057] Steps having a small taper angle can be formed by wet etching ordry etching. For example, in wet etching, since the etching proceedsisotropically, a taper angle of about 45° can naturally obtained if theoveretching time is not set too long. Also, in dry etching, a taperangle of 20° to 30° can easily be obtained by utilizing retreat of aresist due to the etching, that is, by selecting etching conditions suchas a dry etching gas, high frequency (e.g., RF) power and a gas pressureso that a taper angle of the resist is transferred. The etching gas forthis purpose includes gases of hydrogen halides such as hydrogenchloride and hydrogen iodide, a bromine gas, and a methanol gas.

[0058] Films for disposing spacers to be formed in a later process areformed on the ITO films 2. Any insulating film may be used as suchfilms. The films may be formed by various methods: forming inorganicthin films such as SiO₂ films or SiN_(x) films by sputtering or vacuumevaporation, forming SiO₂ films by SOG coating, and applying resist,polyimide, acrylic resin or the like. Since it is necessary to expose aportion of the ITO films 2 formed under the insulating film, theinsulating film needs to be patterned without damaging the ITO films 2.Although there is no limitation on the thickness of the insulatingfilms, when an inorganic thin film is used, the manufacturing cost canbe reduced by decreasing the thickness thereof.

[0059] It is desirable that the ends of the insulating films 3 formedabove the ITO film 2 be also tapered. The taper angle should be about60° or less, preferably 45° or less. When SiO₂ films are formed as theinsulating films 3, a taper angle of 45° can be obtained by wet etchingif the overetching time is not set too long. To make the taper angleeven smaller, dry etching is suitable as in the case of forming the ITOfilms 2. A carbon fluoride type etching gas such as CF₄+O₂ is generallyused.

[0060] In this embodiment, polyimide is used to form the insulatingfilms 3. Non-photosensitive polyimide to be prepared is diluted to about5% with N-methyl pyrrolidone (NMP) or γ-butyrolactone. Such polyimide isapplied by spin coating and then prebaked at 145° C. for one hour. Aftera positive resist is applied, patterning is performed to form astructure shown in FIGS. 3B and 3G.

[0061] Exposed portions of the resist and corresponding portions of thepolyimide film are removed sequentially with an aqueous solution oftetra methyl ammonium hydroxide (TMAH) having a concentration of about2.38%. The TMAH is a developer for the resist. Further, only theremaining portions of the resist are removed by ethanol, to form desiredinsulating films. Although the above description is directed to the caseof using non-photosensitive polyimide, photosensitive polyimide may alsobe used. In this case, no resist is needed.

[0062] The polyimide insulating films 3 thus obtained are completelycured at about 350° C. to prevent them from being affected by a chemicalsolution. Since the insulating films 3 contract in this process, theirsteps come to be tapered.

[0063] When the step shape of the ITO films 2 is hard to control in theabove manner, the photomask may be so designed that the insulating films3 formed in this process also cover the step portions of the ITO films2.

[0064] Subsequently, a spacer film to be used as spacers 4 (see FIG. 1A)is formed. Because of their purpose, the spacers 4 may be either aconductor or an insulator, and have either a single layer or amultilayer structure. However, when the spacers 4 are a conductor, thereis a possibility that metal films formed in a later process cause ashort circuit or a current leak between adjacent display lines via aspacer. This problem may be-solved by making the undercut amount inetching the spacer film sufficiently large.

[0065] The spacer made of a metal has the following advantages. (1)Since the spacer is sufficiently strong and malleable, the elements thatare easily rendered faulty due to the existence of dust can sufficientlybe cleaned with ultrasonic waves, for example. (2) Since the spacer ismore resistant to heat than a resist etc., dehydration can be effectedby heat treatment. (3) Since the spacer is hardly charged, particles areless likely to attach to the spacer. (4) When a short circuit occurs inan element circuit due to dust, the spacer can be burnt off.

[0066] It is necessary to select an etching material for the spacer filmwhich neither etches nor affects the ITO films 2 that are in contactwith the spacer film in etching the spacer film. Also, since the spacerfilm is used to form the spacers 4, it should be so formed as to bethicker than a total thickness of all of the organic EL film 6, thesecond electrode 7, the metal film 8, the protecting film 9, and otherfilms, as shown in FIG. 1B. Thus, it is desirable that the spacer filmbe made of a material which allows easy formation of a thick spacerfilm. As such a material film, an SOG film and a resin film are used.When the spacer film is made of a metal material, a laminate structureof a Cr film, a Ti film, a TiN film, or other film as an etching barrierfilm for the ITO films 2 and an Al film or other film which has a highformation rate may be formed. The etching barrier film is not limited toa metal material.

[0067] When the spacer film is made of polyimide, polyimide whoseconcentration has adjusted to 15% is spin-coated at a thickness of 2 μm,and then prebaked at 145° C. for one hour to form a spacer film 4′ (seeFIGS. 3C and 3H). The thickness of the spacer film 4′ can be adjusted bythe polyimide concentration and the rotational speed of the spin coater.

[0068] After the formation of the spacer film 4′, a positive resist isapplied. When the thickness of the positive resist is 1 μm or more,desirably 2 μm or more, a highly viscous resist is used or therotational speed of the spin coater is set low.

[0069] Since the positive resist is relatively fragile, the method offorming a thick resist is used in this embodiment. However, as shown inFIG. 20, no such method is needed if a harder film (a second spacer) 64is formed under the resist 65 to support the resist 65. The use of theharder film 64 as a support film has another advantage that heattreatment for eliminating water can be performed in a later process.Conversely, if heat treatment is performed without forming the supportfilm, the resist becomes likely to be deformed and undercut regions maybe broken. Note that in FIG. 20, numeral 60 is a substrate, 61 is an ITOfilm, 62 is an insulating film, and 63 is a spacer (a first spacer).

[0070] A conductor such as Cr, Ti, TiN, W, Mo, Ta, ITO, SnO₂ or ZnO, aninorganic insulator such as SiN_(x), SiO₂, diamond like carbon (DLC),Al₂O₃, Ta₂O₅, or glass, a semiconductor such as Si or SiC, or othermaterials can be used to form the harder film 64.

[0071] The harder film 64 can be formed by sputtering, vacuumevaporation, plating, plasma chemical vapor deposition (CVD), thermalCVD or the like. In the spacer formed by a thin film having a pluralityof layers, when one layer which is in contact with a photosensitivematerial constituting the resist is not overetched, it can be used asthe support film for the photosensitive material. The photosensitivematerial can be removed, and in this case a substrate can be baked at aheat resistant temperature of the photosensitive material or a highertemperature. Thus, it is advantages in the case that dehydration processfor a substrate can be performed.

[0072] As described above, by applying the-positive resist and thenperforming exposure and development to form a desired photopattern,cap-shaped (an overhanging structure in general) photosensitive films(photosensitive resin films) 5 are formed as shown in FIGS. 3D and 3I.The portions of the polyimide spacer films 4 which are exposed when thepositive resist is developed are subsequently removed by using thedeveloper, to form spacers 4 as shown in FIGS. 3E and 3J.

[0073] The development time is determined in accordance with theundercut amount (i.e., undercut length) of the polyimide spacer film 4′.The undercut amount is greatly influenced by the polyimide prebakingtemperature and time. In particular, the prebaking temperature needs tobe controlled so as to make the thickness of the spacer film 4′ uniformover the entire substrate surface. In this embodiment, the developmenttime is so controlled that the undercut length becomes about 4 μm. Thus,a structure shown in FIG. 3E is formed. Note that in FIG. 1A, anundercut length 39 is a length from the side surface of the spacer 4 tothe lower edge of the photosensitive film 5.

[0074] A structure shown in FIG. 4A is formed by consecutivelyevaporating, without exposure to the air, i.e., in a vacuum,N,N′-bis(m-methyl phenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine(hereinafter referred to TPD; see FIG. 15) as a hole injectionlayer/hole transport layer of the organic EL film 6,tris(8-hydroxyquinoline) aluminum (hereinafter referred to Alq₃; seeFIG. 16) as a light emitting layer/electron transport layer of theorganic EL film 6, and an Mg/Ag alloy (weight ratio: 10:1) film as thesecond electrode 7. The thickness of each of the TPD layer and the Alq₃layer constituting the organic EL film 6 is 500 angstrom and thethickness of the Mg/Ag alloy film constituting the second electrode 7 is2,000 angstrom.

[0075] In the invention, the constituent films of the organic EL elementand the order of laying those films are not limited to those of thisembodiment. The hole injection layer, the light emitting layer, and thesecond electrode may be made of materials other than the above ones. Ahole injection layer, an electron transport layer, an electron injectionlayer, and other layers may additionally be formed to provide multilayerstructures.

[0076] In order to form the organic EL films 6, the second electrodes 7,and other layers only on the light emitting portion (i.e., displayscreen portion), the evaporation is performed by using a metal mask thatis mounted on a substrate holder of an evaporation apparatus.

[0077] As shown in FIGS. 4A and 4B, after the formation of the organicEL films 6 and the second electrodes 7, the substrate is transferredwithout exposing to the air, i.e., in a vacuum, to a vacuum chambercapable of film formation by sputtering, so that the metal films 8 suchas Al films are formed by sputtering. In this process, it is importantthat the metal films 8 be formed by a method that can provide superiorstep coverage to the method by which the organic EL films 6 havingorganic EL layers are formed. In this manner, the Al films are alsoformed in the undercut regions, so that the organic EL films 6 which arenot resistant to water and oxygen are completely shielded from the air.

[0078] The above process provides a notable advantage that the organicEl, films 6 can be shielded from an organic solvent used in etching, aswell as from water and oxygen. In the conventional structure, the entireorganic EL film is removed by an organic solvent that has soaked into itfrom an exposed portion of the film at an end portion of the pattern,for example. Thus, once the organic EL film is formed, it is prohibitedto be in contact with any organic solvent, which restrict the kinds ofusable manufacturing processes. In contrast, the invention allows use ofa variety of manufacturing processes.

[0079] To further improve the resistance to water and an organicsolvent, the protecting films 9 such as SiO₂ films may be formed asshown in FIG. 4B after the metal films 8 made of a stable metal such asaluminum are formed.

[0080] In this embodiment, Al films are formed at a sputtering pressureof 8×10⁻³ torr. The sputtering pressure is desired to be as high aspossible. This is because if the sputtering pressure is higher, Al atomsemitted from the Al target to various directions more likely collidewith argon atoms and are scattered, so as to go into the undercutregions more likely, whereby the organic EL films 6 are sufficientlycovered with the Al films. That is, the mean free path of Al atomsshould be shorter than the distance between the target and thesubstrate. On the other hand, if the sputtering pressure is high, theformation rate decreases due to a reduction in the voltage applied tothe target and the scattering of Al atoms. Thus, the sputtering pressureis determined by a balance between the productivity and the stepcoverage.

[0081] Although in this embodiment the metal films 8 of a stable metalsuch as aluminum are formed by sputtering, the invention is not limitedto such a case. For example, similar advantages are obtained by methodscapable of providing good step coverage such as a method in whichevaporation is performed in a low vacuum with introduction of an inertgas, plasma CVD, and photo-assisted CVD. The same methods apply to theformation of the SiO films as the protecting films 9.

[0082] By the way, when lead out Al electrode pads (not shown) areformed to connect a control integrated circuit (IC) to the metal films 8which are in contact with the second electrodes 7, the lead out Alelectrode pads are arranged at side portions of the display portion soas not to cause defect portions on the display portion. To prevent theconstituent films of the organic EL elements and the SiO₂ films frombeing formed below and above the Al electrode pads, respectively, the Alelectrode pads are shielded by the metal masks in forming theconstituent films of the organic EL elements 6 and the SiO₂ protectingfilms. This is to improve the adhesiveness between the Al electrode padsand the substrate and to prevent insulating films from being formed onthe Al electrode pads. In plasma CVD and photo-assisted CVD which aremuch superior in coverage performance, the SiO₂ films may be formed onthe Al electrode pads even if the metal masks are used. In such a case,connection holes reaching the Al electrode pads may be formed byphotolithography.

[0083] When insulating films such as SiO₂ films are formed as theprotecting films 9 in the final process, even if the resist films, i.e.,the photosensitive films 5 are broken by mechanical pressure, therespective display lines would be still covered with the protectingfilms 9. Thus, if only the resist in the vicinity of the Al electrodepads on which no insulating film is formed is wiped off by using asolvent, failures such as a short circuit via constituent films of theorganic EL elements will not occur without removing the constituentfilms remaining on the resist in the vicinity of the display lines. Theelimination of the process of removing the cap-shaped resist remainingover the entire substrate surface is advantageous in the manufacturingcost.

[0084] To provide more reliable organic EL elements by protecting theorganic EL films from physical contact, pollution, etc., it is desirableto attach a glass substrate or the like to the organic EL elements fromabove (i.e., from the opposite side of a display surface). However, insuch a case, a solvent contained in an adhesive dissolve the resistfilms, i.e., the cap-shaped photosensitive films (photosensitive resinfilms) to possibly cause a short circuit between adjacent organic ELelements if insulating films as the protecting films are not formed inthe final process. Thus, when the glass substrate or the like forprotection is attached to the organic EL elements from above, it isdesirable to remove in advance the constituent films of the organic ELelements and Al films remaining on the photosensitive resin films. Thesefilms can easily be removed by immersing them in a chemical solutionthat can dissolve the photosensitive resin films or the spacers. Astructure shown in FIG. 4C can be formed by removing only thephotosensitive resin films by using an alcohol such as ethanol orisopropyl alcohol, an ester such as butyl acetate or ethyl acetate, oran organic solvent such as acetone or xylene.

[0085] Both the spacers 4 and the photosensitive resin films can beremoved by using a resist removing solution such as NMP,γ-butyrolactone, or type number MS-2001 of Fuji Hant Co., Ltd. which ison the market. In this case, the thin films formed on the photosensitiveresin films are lifted off. By removing also the spacers 4, the thinfilms on the photosensitive resin films 5 can easily be lifted off.Thus, this process is easy on manufacture.

[0086] If the spacers 4 are left as shown in FIG. 4C, they can be usedas posts. That is, when the substrate for protection is attached asdescribed above, since it is not in contact with the organic EL elementsbecause of the existence of the spacers 4, physical influences of thesubstrate on the organic EL elements can be lowered and it isadvantageous on the prolongation of the life of the organic EL elements.

[0087] In this manner, the manufacturing process and the structure ofthe organic EL elements may be determined in accordance with the purposeof manufacturing the organic EL display device, that is, depending onwhich of the manufacturing cost and the life is important.

[0088] In this embodiment, only the photosensitive resin films 5 areremoved and the spacers 4 are left as shown in FIG. 4C. Also, to furtherimprove the water resistance, carbon fluoride polymer films (not shown)are formed on the protecting films 9 by plasma CVD. Film forming gasesof CF₄ and CHF₃ to be used are decomposed at a gas pressure of 100 mtorr to form the carbon fluoride polymer films. Since plasma CVDprovides better coverage performance than sputtering, it is difficult tolift off the photosensitive resin films 5 on the spacers 4 once thecarbon fluoride polymer films are formed.

[0089] The portions of the carbon fluoride polymer films formed on theAl electrode pads are removed by photolithography using enzyme plasma,and then the resist is removed. Thus, a desired organic EL displaydevice is completed.

[0090] In the organic EL display device thus manufactured which issuperior in the resistance to water and an organic solvent, the displaylines are independent of each other and the organic EL films arecompletely covered with the stable thin films. Thus, it has beenconfirmed that the organic EL display device of this embodiment is asreliable as organic EL display devices constituted of conventionalorganic EL elements which operate in a vacuum or a dried nitrogenatmosphere.

Embodiment 2

[0091] FIGS. 5A-5E and 7A-7B show a manufacturing process of an organicEL display device according to a second embodiment of the invention. Thesecond embodiment is directed to the process of manufacturing a simplematrix (multiplex) type display device in which one pixel size is 330μm×110 μm, the number of pixels is 320×240×3 (RGB) dots, and colorfilters are provided. In comparison with the first embodiment, in thisembodiment, a higher resolution display device is manufactured and colorfilters are formed in advance.

[0092]FIG. 6 is a plan view of a color filter portion of the organic ELdisplay device according to the second embodiment of the invention, inwhich the top-right block and the bottom blocks are drawn in white todescribe dimensions of color filters. One pixel has a size of 330 μm×110μm. A TiN film and an Al film are shown as connecting portions C to ITOfilms which portions have a size of 30 μm×30 μm and a line L having awidth of 10 μm. FIGS. 5A-5E and 7A-7B are sectional views taken along adot line A-A′ in FIG. 6.

[0093] As the resolution increases, the electric resistance oftransparent conductive films such as ITO films more likely causes aproblem. To solve this problem, the Al films, whose resistivity is about{fraction (1/100)} of that of the transparent conductive films, are usedto form a laminate structure with the transparent conductive films, tothereby reduce the resistance value. Since direct contact between the Alfilm and the transparent conductive film causes a large contactresistance, it may be better to form a TiN film, a Cr film, or otherfilm between those films.

[0094] An Al film of about 1.5 μm in thickness is formed on atransparent substrate (not shown) such as a glass substrate bysputtering. Immediately thereafter, a TiN film of about 300 angstrom inthickness is formed thereon by sputtering. Thus, a laminate film of theAl film and the TiN film is formed. If the Al film and the TiN film areformed in succession without being exposed to the air, i.e., in avacuum, a native oxide film can be prevented from being formed on asurface of the Al film, so that good contact is obtained between the Alfilm and the TiN film. Instead of the Al film, an Al alloy filmcontaining an element other than aluminum may be used. To prevent unevenportions (hillocks) from being formed on the surface of the Al film dueto crystal growth of aluminum in a later heat treatment process, it isin many cases desirable to use an Al alloy film containing scandium (Sc)or the like.

[0095] The laminate film of the Al film and the TiN film is thenpatterned by photolithography to obtain Al films 11 and TiN films 12formed thereon as shown in FIG. 5A. To obtain a high throughput and agood processed shape, the TiN film and the Al film are etched at thesame time by dry etching.

[0096] The dry etching is reactive ion etching (RIE) in which theelectric power is 2,000 W, the gas pressure is 100 m torr, and etchinggases are Cl₂ and BCl₃. After the etching, ashing is performed withoutexposure to the air, i.e., in a vacuum. This is to prevent corrosion ofaluminum after the dry etching, which is called “after-corrosion.” Wetetching may be performed because a poor processed shape does not causeany serious problems.

[0097] To form color filters, a pigment dispersion type color filterapplication/formation process is performed which is most commonlyemployed as a coloring manner for liquid crystal displays. Applicationconditions for forming RGB (red, green, blue) filters at a thickness of1.0-2.5 μm are determined. In FIG. 5B, red filters 13, green filters 14,and blue filters 15 are patterned to expose the surfaces of the TiNfilms 12.

[0098] For example, the application/formation process of the red filters13 is as follows. After a red filter solution is applied by spin coatingat 1,000 rpm (revolutions per minute) for about 5 seconds, prebaking isperformed at 100° C. for 3 minutes. Then, a photomask is positioned byusing an exposing apparatus, and ultraviolet light of 20 mW/cm² isirradiated for 30 seconds. Subsequently, development is performed withan about 0.1% TMAH aqueous solution. The development time is about oneminute. Further, thermal curing is performed at 220° C. for one hour sothat the red filters 13 thus formed will not be dissolved by filtersolutions of the other colors (green and blue) to be applied in thelater processes.

[0099] Because of the use of different pigments, the conditions forforming the green filters 14 and the blue filters 15 are somewhatdifferent from those for forming the red filters 13. However, the greenfilters 14 and the blue filters 15 may be formed sequentially byapproximately the same processes as the processes for forming the redfilters 13. Thus, the red filters 13, the green filters 14, and the bluefilters 15 are formed as shown in FIG. 5B.

[0100] Although this embodiment relates to the case of forming only thecolor filters because it can be manufactured relatively easily, theinvention is not limited to such a case. For example, fluorescenceconversion filters may be used to output green light and red lightthrough color conversion, to provide more intense light. Further, alaminate structure of color filters and fluorescence conversion filtersmay be formed to prevent reduction in brightness while improving thepurity of colors.

[0101] In order to improve the flatness of the forming surface of an ITOfilm to be formed in a later process, an overcoat material such aspolyimide or acrylic resin is applied to the red filters 13, the greenfilters 14, and the blue filters 15, and then patterning is performed toexpose the surfaces of the TiN films 12. Also, thermal curing isperformed at about 220° C. for one hour, to form overcoat layers 16 asshown in FIG. 5C.

[0102] After the formation of the overcoat layers 16, an ITO film as atransparent conductive film is formed at a thickness of about 1,400angstrom by sputtering. Further, a resist pattern is formed byphotolithography, and then the ITO film is etched with dilutehydrochloric acid. The resist is removed to form an ITO film 17 (seeFIG. 15D). Therefore, a pattern in which the transparent conductive filmand the Al film wiring that is formed to reduce the resistance areconnected to each other is formed to constitute a display line (columnline).

[0103] An SiO₂ film as an insulating film is formed on the patterned ITOfilm 17 by sputtering, and then patterned to remain in the regions otherthan the regions where light emitting portions are seen from the side ofthe glass substrate (not shown), so that SiO₂ films 18 are formed (seeFIG. 5E). By the structure in which the ITO film 17 is covered with theSiO₂ films 18, useless light emission in the regions not seen from theglass substrate side can be avoided. In addition, since holes or groovesare necessarily formed in these regions, an organic EL film such as alight emitting layer evaporated on an inclined portion may be renderedthin, to possibly form a current leak path. Thus, the formation of theinsulating film is desirable.

[0104] Although in this embodiment an SiO₂ film is used as theinsulating film, the invention is not limited to such a case. Since whatis needed is insulation, not only an inorganic insulating film such asan SiO₂ film and an SiN_(x) film but also resin such as polyimide,acrylic resin, and epoxy resin may be used. In patterning the insulatingfilm, if a mask pattern is formed such that insulating films are leftalso in the regions where spacers are to be formed, a process forforming insulating films under a spacer film can be omitted.

[0105] After the patterning of the SiO₂ films 18, resist films 20 havinga cap-shaped structure (overhanging structure in general) are formed onspacers 19 by processes similar to the processes of FIGS. 3C-3E with apolyimide film used as a spacer film (see FIG. 7A).

[0106] For a color display, light emitting elements are constructed byforming the following materials on the structure of FIG. 7A. In thisembodiment, organic EL materials are used which emit white light.

[0107] To form a yellow light emission organic EL film, polythiophene(see FIG. 17) is evaporated at a thickness of 100 angstrom as a holeinjection layer, and then TPD doped with rubrene (see FIG. 18) at 1weight % is coevaporated at a thickness of 500 angstrom as a holetransport layer/yellow light emission layer. It is preferable that theconcentration of rubrene be in a range of 0.1 to 10 weight %, in thisrange high efficiency light emission is attained. The rubreneconcentration, which may be determined in accordance with the colorbalance of light emission colors, depends on the light intensity and thewavelength spectrum of a blue light emission layer to be formed in alater process. To form a blue light emission organic EL film, 4,4′-bis[(1, 2, 2-trisphenyl)ethenyl]-biphenyl (see FIG. 19) is evaporated at athickness of 500 angstrom as a blue light emission layer, and then Alq₃is evaporated at 100 angstrom as an electron transport layer. They areevaporated in succession without being exposed to the air, i.e., in avacuum. Thus, organic EL films 21 are formed.

[0108] Further, an Mg/Ag alloy (weight ratio: 10:1) film is evaporatedat a thickness of 2,000 angstrom as second electrodes 22 without beingexposed to the air, i.e., in a vacuum. Then, Al films 23 and SiO₂protecting films 24 are formed in succession by sputtering in the samemanner as in the processes of FIGS. 4B and 4C.

[0109] Finally, the resist films 20, the various thin films formedthereon, and the spacers 19 are removed by a removing solution, toprovide a desired simple matrix organic EL display device as shown inFIG. 7B.

[0110] According to this embodiment, since the evaporation method can beone in which the uniformity of films are regarded as important, theyield can be increased and the light emission characteristic can be madeuniform.

[0111] Conventionally, a material not resistant to water or oxygen isnecessarily exposed to the air even temporarily, which decreases thereliability of organic EL elements thereby. In contrast, the inventioncan provide organic EL elements with very high reliability because theorganic EL film can be completely covered with a material that is stablewith respect to water and oxygen on each display line (pixel line).

[0112] Numerical values used in the invention are merely examples andthe invention is not limited to those values.

[0113] According to the invention, the overhanging portions wider thanthe spacers can easily be formed by overetching. By the existence of theoverhanging portions, the organic EL elements can be isolated easily.

[0114] According to the invention, since only the overhanging portionsformed on the spacers can be removed, a sealing glass substrate or thelike for sealing the entire device can easily be provided over theorganic EL elements.

[0115] According to the invention, since not only the overhangingportions but also the spacers can be removed, even an adhesivecontaining a solvent capable of dissolving a resist or the like can beused as the adhesive for adhering a sealing glass substrate or the liketo the device. This allows selection of an adhesive from a wide varietyof and various kinds of adhesives.

[0116] Further, according to the invention, the protecting filmsconstructed by at least one of an insulating film and a metal film whichis stable with respect to oxygen, water and organic solvents can beformed on the second electrodes by using a method that can providebetter step coverage than methods for forming the organic films and thesecond electrodes. This allows photolithography to be conductedthereafter. Thus, the embodiment enables manufacture of an organic ELdisplay device having very high reliability and a long life.

Embodiment 3

[0117] FIGS. 13A-13C and 14A-14C are plan pattern views and sectionalviews of a light emitting portion of an organic EL display device havingelement isolating structure portions formed therein according to theinvention. If the element isolating structure portions as shown in FIG.1A are formed straight, the element isolation can be effected with avery high yield. However, in FIG. 13B that is a sectional view takenalong a dot chain line B-B′ in FIG. 13A, the undercut length tends to beshort in a region inside a portion of an element isolating structureportion 121 where it is bent at 90° or less or a region inside itscurved portion having a small curvature. As a result, there may occur acase that the light emitting portion and the element isolating structureportion are short-circuited with each other via a metal film 116 made ofa stable metal that is hardly affected by water, oxygen, and organicsolvents. This will cause a reduction in yield.

[0118] That is, in the case wherein light emitting portions 120 a and120 b are isolated from each other by the element isolating structureportion 121 having an overhanging structure of FIG. 13A, if the bendingportions have an angle of 90° or less, the undercut length becomes veryshort in the regions inside the bending portions as indicated by a dotline in the enlarged part of FIG. 13A. As a result, when an organic ELfilm 114, a second electrode 115, a metal film 116, and other films areformed in each of the light emitting portions 120 a and 120 b, the metalfilm 116 is formed also on the side surface of a spacer 112 in theundercut region where the undercut length is very short as shown in FIG.13B. In this manner, the metal film 116 formed above a resist 113 andthe light emitting portion 120 a and 120 b are connected to each other.

[0119] The short circuit may also occur in a region inside a curvedbending portion of the element isolating structure portion which has aradius of curvature of 5 μm or less.

[0120] When the element isolating structure portion 121 is formedstraight as in a portion indicated by a dot chain line A-A′ in FIG. 13A,the undercut length of the spacer 112 is proper as shown in FIG. 13Cthat is a sectional view taken along line A-A′ in FIG. 13A. Since themetal film 116 is not formed on the side surface of the spacer 112 so asto assume a thick film, the metal films 116 formed above and below theresist 113 are not short-circuited with each other.

[0121] Conversely, in a region outside a bending portion (90° or less)of the element isolating structure portion 121 (see FIG. 14A), anundercut region 117 becomes extremely long as shown in FIG. 14B that isa sectional view taken along a dot chain line B-B′ in FIG. 14A. As aresult, when the overhanging body of the element isolating structureportion 121 is constituted only of a resist 113, the overhanging bodylikely hangs down as shown in FIG. 14C. This may cause a short circuitbetween the metal films 116 which are formed on the light emittingportion and the outside portion of the element isolating structureportion 121 when the metal films 116 are formed.

[0122] To reduce the number of lead out electrodes of a display devicehaving complicated patterns, it is necessary to form element isolatingstructure portions that meander. It is desired to increase the yield informing those element isolating structure portions.

[0123] When a bending portion of the element isolating structure portionhas an angle of 90° or less or it is curved at a small radius ofcurvature of 5 μm or less, the reason why the undercut length varieswith the shape of the plan pattern is considered non-uniformity in thedegree of the action that an etching chemical goes around to act on thespacer film. Thus, in a region where the undercut length tends to beshort, it is expected that the non-uniformity can be avoided byemploying a plan pattern that allows an etching chemical to go aroundmore easily.

[0124] It has been confirmed that a marked increase in yield can beobtained by forming a photomask pattern that is free of a portion wherethe element isolating structure portion is bent at a small angle of 90°or less as a simplest but effective method for attaining a plan patternthat allows an etching chemical to go around more easily in undercuttingthe spacer film.

[0125] Although a pattern bending angle larger than 90° is effective,the bending angle should be 100° or more and, more desirably, 135° ormore. In experiments, portions having a bending angle of 135° show adifference in undercut length of only 30% as compared to straightportions. That is, it has been confirmed that the undercut lengthdecreases by 30% in regions inside such bending portions from that ofthe straight portions, and that it increases by 30% in regions outsidethe bending portions.

[0126] When an organic EL display device having the element isolatingstructure portions on a substrate is manufactured by using the abovedescribed pattern, no short circuit is observed in the bending portions.A similar increase in yield is obtained by forming circular arc patternshaving radii of curvature that are larger than 5 μm.

[0127] The third embodiment of the invention will be described in a morespecific manner with reference to FIGS. 9A and 9B, which are planpattern views and sectional views of light emitting portions of anorganic EL display device according to the third embodiment of theinvention. In FIG. 9A, an element isolating structure portion 31isolates light emitting portions 32 a and 32 b constituted of organic ELfilms and other films. The element isolating structure portion 31 iscomposed of a resist 33 and a spacer 34, and regions inside its bendingportions are bent at an angle of 135°.

[0128] In FIG. 9B that is a sectional view taken along a dot chain lineA-A′ in FIG. 9A, the regions inside and outside the spacer 34 which areformed under the resist 33 have sufficiently long undercut lengths ofabout 3 μm and about 4 μm, respectively. Thus, no short circuit occurswhen a metal wiring film is formed on this structure.

[0129] As described above, according to the invention, a flat paneldisplay using organic EL elements which can be manufactured at a stable,high yield and enables various lighting patterns is obtained.

Embodiment 4

[0130]FIGS. 10A and 10B are plan pattern views and sectional views oflight emitting portions of an organic EL display device according to thefourth embodiment of the invention. In FIG. 10A, an element isolatingstructure portion 31′ isolates light emitting portions 32 a′ and 32 b′constituted of organic EL films and other films. The element isolatingstructure portion 31′ is composed of a resist 33′ and a spacer 34′, andregions inside its bending portions assume circular arcs having a radiusof 10 μm.

[0131] In FIG. 10B that is a sectional view taken along a dot chain lineA-A′ in FIG. 10A, the regions inside and outside the spacer 34′ formedunder the resist 33′ have sufficiently long undercut lengths of about 3μm and about 4 μm, respectively. Thus, no short circuit occurs when ametal wiring film is formed on this structure.

Embodiment 5

[0132] FIGS. 11A-11C are plan pattern views of a display portion of anorganic EL display device according to a fifth embodiment of theinvention, and FIGS. 12A-12H are plan pattern views and sectional viewsof a bar graph portion of the display portion of the above organic ELdisplay device. The fifth embodiment is directed to a case ofmanufacturing a 2-digit digital counter with a bar graph.

[0133]FIG. 11A is a view of a 2-digit digital counter as viewed from theorganic EL film side (i.e., the bask side) rather than from thetransparent substrate side (i.e., the display side), and is hence amirror image of an ordinary view as viewed from the display side. FIG.11A also shows light emitting regions as viewed from the organic EL filmside.

[0134]FIG. 11B shows a relationship between the pattern of ITO films(indicated by dot lines) formed on a substrate 40 and openings (wherethe ITO films are exposed; indicated by solid lines) that are obtainedby partially removing an insulating film formed on the ITO films.

[0135]FIG. 11C shows element isolating structure portions 41 a and 41 b,an area E where organic EL films and second electrode portions areformed, and an area S where metal wirings made of a stable metal hardlyaffected by water, oxygen, and organic solvents and protecting films areformed. The element isolating structure portion 41 a isolates the bargraph from the numeral displaying portion as well as isolates the bargraph into two sections. The element isolating structure portion 41 bencloses the numeral display portion.

[0136] After the openings (indicated by solid lines) are formed bypartially removing the insulating film formed on the pattern of the ITOfilms (indicated by dot lines) as shown in FIG. 11B, the elementisolating structure portions 41 a and 41 b are formed as shown in FIG.11C. As described later, the element isolating structure portions 41 aand 41 b are formed with a pattern in which every bending portion has abending angle of 135°. The element isolating structure portion 41 aincludes a slant straight portion 41 a′ formed at the center of the2-figure bar graph.

[0137] After the element isolating structure portions 41 a and 41 b areformed, organic EL films and second electrodes containing a metal havinga small work function are formed by evaporation in the area E indicatedby the dot chain line, and metal films and protection films are formedin the area S indicated by the two-dot chain line (see FIG. 11C). Atthis time, a common electrode C1 is connected to the metal film of theelement isolating structure portion 41 a-1 located on the right side ofthe slant straight portion 41 a′, and a common electrode C2 is connectedto the metal electrode of the element isolating structure portion 41 a-2located on the left side of the slant straight portions 41 a′. A commonelectrode C3 is connected to the metal electrode of the elementisolating structure portion 41 b.

[0138] A manufacturing process of the bar graph will be described withreference to FIGS. 12A-12H. FIGS. 12A-12D are plan views of the bargraph pattern, and FIGS. 12E-12H are sectional views taken along dotchain lines A-A′, B-B′, C-C′, and D-D′ in FIGS. 12A-12D, respectively.

[0139] An inexpensive soda glass substrate is used as a substrate 40 foran organic EL display device. A silica coating is performed for theentire surface of the substrate 40. The silica coating prevents sodiumfrom being eluted from the glass substrate when it is heated, protectsthe soda glass substrate that is not resistant to acids and alkalis, andimproves the flatness of the glass substrate surface.

[0140] Next, an ITO film which is a transparent conductive film as afirst electrode is formed at a thickness of 1,000 angstrom on the glasssubstrate 40 by sputtering. The use of the ITO film is due to the factthat it exhibits superior characteristics to films made of othermaterials when used as a transparent conductive film. However, atransparent electrode of a ZnO film, SnO₂ film, or the like may also beused if it has transmittance and resistivity, for example, that will notcause any problem during use. When the ITO film is formed over a largearea, sputtering is advantageous in uniformity and film quality of aresulting film as well as productivity. The ITO film need not always beformed by sputtering, and may be formed by evaporation, for example.

[0141] After a resist pattern is formed on the formed ITO film byphotolithography, unnecessary portions of the ITO film are removed byetching and then the resist is removed, to leave a desired electrodepattern of the ITO film 41 (see FIGS. 12A and 12E).

[0142] Next, a film for determining the light emitting regions is formedon the ITO film 41. Any insulating film may be used as this film. Thefilm may be formed by various methods: forming an inorganic thin filmsuch as an SiO₂ film or an SiN_(x) film by sputtering or vacuumevaporation, forming an SiO₂ film by SOG coating, and applying resist,polyimide, acrylic resin, or the like. Since it is necessary to expose aportion of the ITO films 41 formed under the insulating film, theinsulating film needs to be patterned without damaging the ITO film 41.Although there is no limitation on the thickness of the insulating film,when an inorganic thin film is used, the manufacturing cost can bereduced by decreasing the thickness thereof.

[0143] In this embodiment, polyimide is used to form the insulatingfilm. Non-photosensitive polyimide to be prepared is diluted to about 5%with NMP or γ-butyrolactone. Such polyimide is applied by spin coating,and then prebaked at 145° C. for one hour. After a positive resist isapplied, patterning is performed (see FIGS. 12B and 12F).

[0144] Exposed portions of the resist and corresponding portions of thepolyimide film are removed sequentially-with an aqueous solution of TMAHhaving a concentration of about 2.38%. TMAH is a developer for theresist. Further, only the remaining portions of the resist are removedby ethanol, to form a desired insulating film 42. Although the abovedescription is directed to the case of using non-photosensitivepolyimide, photosensitive polyimide may also be used. In this case, noresist is needed.

[0145] The polyimide insulating film 42 thus obtained is completelycured at a temperature not higher than 350° C. so as not to be affectedby chemical solutions to be used in later process. Since the insulatingfilm 42 contract at this time, the steps are tapered. Thus, a patternfor exposing only the light emitting portions and connecting portions toexternal circuits is obtained (see FIG. 12B)

[0146] Subsequently, a spacer film to be used as a spacer 43 is formed(see FIG. 12G). Because of their purpose, the spacer 43 may be either aconductor or an insulator, and have-either a single layer or multilayerstructure. However, when the spacer 43 is a conductor, there is apossibility that metal films formed in a later process cause a shortcircuit or a current leak between adjacent display lines via a spacer43. This problem may be solved by making the undercut amount in etchingthe spacer film sufficiently large.

[0147] As described above, the spacer made of a metal has the followingadvantages. (1) Since the spacer is sufficiently strong and malleable,the elements that are easily rendered faulty due to the existence ofdust can sufficiently be cleaned with ultrasonic waves, for example. (2)Since the spacer is more resistant to heat than a resist etc.,dehydration can be effected by heat treatment. (3) Since the spacer ishardly charged, particles are less likely to attach to the spacer. (4)When a short circuit occurs in an element circuit due to dust, thespacer can be burnt off.

[0148] It is necessary to select an etching material for the spacer filmwhich neither etches nor affects the ITO film 41 that are in contactwith the spacer film in etching the spacer film. Also, since the spacerfilm is used to form the spacer 43, it should be so formed as to bethicker than all of an organic EL film, a second electrode, a protectingfilm, and other films. Thus, it is desirable that the spacer film bemade of a material which allows easy formation of a thick spacer film.Examples of such a film are an SOG film and a resin film. When thespacer film is made of a metal material, a laminate structure of a Crfilm, a Ti film, a TiN film, or other film as an etching barrier filmformed on the ITO film 41 to prevent their etching and an Al film orother film which has a high formation rate may be formed. The etchingbarrier film is not limited to a metal material.

[0149] When polyimide is used to form the spacer 43, polyimide whoseconcentration has been adjusted to 15% is spin-coated at a thickness of2 μm, and then prebaked at 145° C. for one hour. The thickness ofpolyimide can be adjusted by the concentration of the solution to beapplied by spin coating and the rotational speed of the spin coater. Thepolyimide film can be made thicker by increasing the concentration ordecreasing the rotational speed.

[0150] Subsequently, a positive resist is applied to the prebakedpolyimide film. When the thickness of the positive resist is not lessthan 1 μm, desirably not less than 2 μm, a highly viscous resist is usedor the rotational speed of the spin coater is set low.

[0151] Since the positive resist is relatively fragile, the method offorming a thick resist is employed in this embodiment. However, no suchmethod is needed if a harder film is formed and then a resist is appliedthereon, i.e., if a harder film is formed under the resist to supportthe resist, as described above. That is, it is not necessary to increasea thickness of the resist. The use of the harder film such as a supportfilm has another advantage that a dehydration treatment by heating foreliminating water absorbed on the substrate surface can be performed ina later process. Conversely, if a heat treatment is performed withoutformation of the support film, the resist becomes likely to be deformedand undercut regions may be broken. Further, if the support film is madeeven stronger, since the overhanging portions remain even after removalof the resist, dehydration by heating the substrate to a temperature nolower than the maximum heat resistant temperature of the resist can beperformed. Thus, as described above, the structure as shown in FIG. 20can be also formed so that the harder film 64 as the support filmsupports the resist 65 as a photosensitive material.

[0152] Exposure and development are performed to form a desiredphotolithography pattern of the element isolating structure portion 41a. Portions of the polyimide film which are exposed by this resistdevelopment are also removed subsequently to the removal of the resist.

[0153] As shown in FIG. 12C, even in bending portions of the patternwhich may be given an angle of 90°, the number of bending portions isincreased to provide larger bending angle. That is, the patterning is somade that the bending portions have a bending angle of 135°.

[0154] The undercut amount of the polyimide film formed under the resistis determined based on the development time. The undercut amount is alsogreatly influenced by the polyimide prebaking temperature and time. Inparticular, it is necessary to control the prebaking temperature so thatthe film quality of the polyimide film be uniform over the entiresubstrate surface. In this embodiment, the development time is sodetermined that the undercut length becomes about 4 μm. In this manner,as shown in FIG. 12G, an element isolating structure portion having thepolyimide spacer 43 and a resist 44 is formed similar to that of FIG.1A.

[0155] Next, TPD as a hole injection layer/hole transport layer of anorganic EL film, Alq₃ as a light emitting layer/electron transport layerof the organic EL film, and an Mg/Ag alloy (weight ratio: 10:1) film asa second electrode are consecutively evaporated in a consecutiveevaporation chambers without being exposed to the air, i.e., in avacuum. The thickness of each of the TPD layer and the Alq₃ layer is setat 500 angstrom and the thickness of the Mg/Ag alloy layer is set at2,000 angstrom.

[0156] In the invention, the constituent films of the organic EL elementand the order of laying those films are not limited to those of thisembodiment. The hole injection layer, the light emitting layer, and thesecond electrode may be made of materials other than the above ones. Ahole injection layer, an electron transport layer, an electron injectionlayer, and other layers may additionally be formed to provide laminatestructures. Further, the thicknesses of the respective films are notlimited to those of the embodiment. That is, the invention is applicableirrespective of the kinds of film forming materials and the structure ofthe films.

[0157] The respective films of TPD, Alq₃, and the second electrode areformed only in the area E by using a metal mask provided in theevaporation apparatus. In FIGS. 12D and 12H, an organic EL constituentfilm 45 including the organic light emitting layer includes organicfilms such as TPD and Alq₃ and the second electrode.

[0158] After the evaporation of TPD serving as the hole injectionlayer/hole transport layer, Alq₃ serving as the light emittinglayer/electron transport layer, and the second electrode, a TiN film andan Al film are formed in succession by sputtering without being exposedto the air, i.e., in a vacuum, to form a metal wiring film 46 (see FIG.12H). The TiN film is formed between the Al film and the patterned ITOfilm as the connection electrode terminal to improve the contactperformance between those films.

[0159] The metal wiring film 46 is formed via the metal mask. Theopening size of the metal mask is so designed that the metal wiring filmis not formed on the portions where lead out wirings for the ITO filmlocated outside the area enclosed by the two dot chain line (see FIG.11C) are connected to external circuits. Thus, the metal wiring film 46is formed only in the area S enclosed by the two dot chain line in FIG.11C.

[0160] The resulting digital counter with the bar graph is divided bythe element isolating structure portions 41 a-1, 41 a-2, and 42 a. Thethree second electrodes are provided therein (see FIG. 11C). The commonelectrode C3 for numeral display is always grounded electrically. Thecommon electrodes C1 and C2 are supplied with a voltage having anoperation frequency of 60 Hz and a duty ratio of ½; that is, they aresupplied with the grounding voltage and the same voltage as the firstelectrode alternately.

[0161] When the common electrode is not divided, the number of electrodeterminals connected to the bar graph portion is the same as the numberof electrode terminals connected to the numeral display portion, i.e.,10. In this case, the common electrode is shared by the bar graphportion and the numeral display portion. On the other hand, if thecommon electrode is divided, the number of total terminals can be made7:5 terminals that are connected to the first electrodes plus 2terminals for the common electrodes C1 and C2. As such, the invention iseffective in dividing common electrodes of various shapes with a highyield.

[0162] Although this embodiment is directed to the case where thebending portions of the plan pattern of the element isolating structureportions have an angle larger than 90°, the same advantages can beobtained even in a case where the bending portions of the plan patternare so formed as to assume circular arcs having a radius of curvaturelarger than 5 μm.

[0163] As described above, by etching the spacer film so that theundercut length does not have a large variation (the uniformity of theundercut length is improved) in the regions inside and outside thebending portions of the plan pattern of the element isolating structureportions, overhanging portions are overhang by a sufficient amount inthe above inside and outside regions. Thus, organic EL elements can beisolated certainly.

[0164] The invention provides the following superior advantages:

[0165] (1) Since the bending portions of the plan pattern of the elementisolating structure portions having an overhanging structure have angleslarger than 90°, the yield of element isolation can be increasedremarkably. If the angles of the bending portions are made 135° or more,the element isolating structure portions can be formed while a shortcircuit is completely avoided in the bending portions.

[0166] (2) Since the bending portions of the plan pattern of the elementisolating structure portions are formed by circular arcs having radii ofcurvature larger than 5 μm, the yield of element isolation can beincreased remarkably. If the radii of curvature of the circular arcs ofthe bending portions are 10 μm or more, the element isolating structureportions can be formed while a short circuit is completely avoided inthe bending portions.

[0167] (3) Since the uniformity of the undercuts of the elementisolating structure portions are greatly improved, an organic EL displaydevice can be manufactured at a high yield. Further, since the secondelectrodes of various shapes which are isolated electrically can beformed, an organic EL display device of the invention can be applied toproducts of various kinds of display method.

What is claimed is:
 1. An organic electroluminescence display devicecomprising: a first electrode which is transparent and formed on asubstrate; an insulating film selectively formed on the first electrode;a plurality of spacers formed on the insulating film; an overhangingfilm which is formed on each spacer and has a width wider than that ofeach spacer; an organic electroluminescence film formed on the firstelectrode and between adjacent spacers; and a second electrode formed onthe organic electroluminescence film.
 2. The device of claim 1 whereinthe spacers comprise a metal.
 3. The device of claim 2 furthercomprising a protecting film which includes at least one selected fromthe group having a metal and an insulating film and covers the secondelectrode.
 4. The device of claim 3 wherein an undercut length of thespacers is determined so that the protecting film including a metal isnot in contact with a side surface of the spacers.
 5. A method forproducing an organic electroluminescence display device, comprising thesteps of: forming a first electrode which is transparent on a substrate;selectively forming an insulating film on the first electrode; forming aspacer film on the insulating film; selectively forming a photosensitivefilm on the spacer film; forming a plurality of spacers by overetchingthe spacer film, so that the photosensitive film overhangs each spacer;forming an organic electroluminescence film on the first electrode andbetween adjacent spacers; and forming a second electrode on the organicelectroluminescence film.
 6. The method of claim 5 wherein the spacerscomprise a metal.
 7. The method of claim 6 further comprising the stepof forming a protecting film which includes at least one selected fromthe group having a metal and an insulating film and covers the secondelectrode.
 8. The method of claim 7 wherein the spacer film isoveretched by an undercut length that the protecting film including ametal is not in contact with a side surface of the spacers.
 9. Themethod of claim 8 further comprising the step of removing thephotosensitive film which overhangs the spacers.
 10. The method of claim7 wherein the organic electroluminescence film, the second electrode andthe protecting film are formed without exposing to an air.
 11. Themethod of claim 9 further comprising the step of removing the spacersafter the photosensitive film removing step.
 12. An organicelectroluminescence display device comprising: a plurality of organicelectroluminescence elements; and an element isolating structure portionwhich is formed between adjacent organic electroluminescence elementsand has an overhanging portion, wherein a bending portion of the elementisolating structure portion has a bending angle larger than 90°.
 13. Thedevice of claim 12 wherein the element isolating structure portionfurther comprises a spacer which is formed under the overhanging portionand includes a metal.
 14. An organic electroluminescence display devicecomprising: a plurality of organic electroluminescence elements; and anelement isolating structure portion which is formed between adjacentorganic electroluminescence elements and has an overhanging portion,wherein a bending portion of the element isolating structure portion isformed by an arc having a radius of curvature of 5 μm or more.
 15. Thedevice of claim 14 wherein the element isolating structure portionfurther comprises a spacer which is formed under the overhanging portionand includes a metal.
 16. A method for producing an organicelectroluminescence display device having an element isolating structureportion formed between adjacent organic electroluminescence elements, abending portion of the element isolating structure portion having abending angle larger than 90°, the method comprising the steps of:forming a first electrode which is transparent on a substrate;selectively forming an insulating film on the first electrode; forming aspacer film on the insulating film; selectively forming a photosensitivefilm on the spacer film; forming a plurality of spacers overhung by thephotosensitive film by overetching the spacer film, to obtain theelement isolating structure portion; forming an organicelectroluminescence film on the first electrode and between adjacentspacers; and forming a second electrode on the organicelectroluminescence film.
 17. The method of claim 16 wherein the spacerscomprise a metal.
 18. The method of claim 17 further comprising the stepof forming a protecting film which includes at least one selected fromthe group having a metal and an insulating film and covers the secondelectrode.
 19. The method of claim 18 wherein the spacer film isoveretched by an undercut length that the protecting film including ametal is not in contact with a side surface of the spacers.
 20. Themethod of claim 19 further comprising the step of removing thephotosensitive film which overhangs the spacers.
 21. The method of claim20 further comprising the step of removing the spacers after thephotosensitive film removing step.
 22. The method of claim 18 whereinthe organic electroluminescence film, the second electrode and theprotecting film are formed without exposing to an air.
 23. An organicelectroluminescence display device comprising: a first electrode whichis transparent and formed on a substrate; an insulating film selectivelyformed on the first electrode; a plurality of first spacers formed onthe insulating film; a plurality of second spacers formed on the firstspacers; an overhanging film which is formed on each second spacer andhas a width wider than that of each first spacer; an organicelectroluminescence film formed on the first electrode and betweenadjacent first spacers; and a second electrode formed on the organicelectroluminescence film.
 24. The device of claim 23 wherein the firstspacers comprise a metal.
 25. The device of claim 23 wherein each secondspacer supports the overhanging film and includes a harder film than theoverhanging film.
 26. A method for producing an organicelectroluminescence display device, comprising the steps of: forming afirst electrode which is transparent on a substrate; selectively formingan insulating film on the first electrode; forming a spacer film havinga plurality of layers on the insulating film; selectively forming aphotosensitive film on the spacer film; forming a plurality of spacersby overetching one layer of the spacer film which is not in contact withthe photosensitive film, so that the photosensitive film overhangs eachspacer; forming an organic electroluminescence film on the firstelectrode and between adjacent spacers; and forming a second electrodeon the organic electroluminescence film.
 27. The method of claim 26wherein the spacers comprise a metal.
 28. The method of claim 26 whereinanother layer of the spacer film which is in contact with thephotosensitive film supports the photosensitive film and includes aharder film than the photosensitive film.